Over the past few years there has been rapidly growing interest in the chemical modification of polymers. This interest can be roughly divided into two main areas. The first area is concerned with the chemical modification of bulk polymers. This type of modification usually is concerned with some property alteration of the original, i.e., decreased flamability, increased solvent resistance, change in gas permeability, etc.
The second area is somewhat more specialized and deals with the preparation of polymer bound catalysts, reagents, protecting groups and chromatography supports. These polymers are usually insoluble, i.e., cross-linked.
A basic problem in the field of polymer modification is one of proper design and control of the polymer system. At present there are only two approaches to modified polymer design:
(1) polymerize or copolymerize suitable monomers containing the desired functionality; or
(2) introduce the desired functionality into a pre-synthesized polymer via some chemical reaction.
The first method though simple in concept has some inherent limitations. The monomers may not be compatible with the polymerization processes or the desired monomer may be difficult or impossible to synthesize.
The second method, polymer functionalization, can normally be accomplished by one of three synthetic pathways or a combination thereof:
(1) modification of a conventional polymer by some suitable reagent, i.e., chloromethylation of polystyrene;
(2) preparation and copolymerization of monomers containing groups which, though inert to polymerization processes, can be easily converted to the desired functions by conventional means, i.e., synthesis of polymers containing pendant phenolic groups can be obtained via hydrolysis of the polymeric acetate derivative; or
(3) synthesis of polymers with functional groups capable of reacting selectively and quantitatively with reactive small molecules, i.e. the reaction of a polymer containing free carboxyl groups with alcohols or amines to yield polymeric esters or amides, respectively.
D. Braun and H. G. Keppler, Makromolekulare Chem. 82, 132 (1965) disclose the preparation of polystyrene with free vinyl groups in the para position via splitting off HBr from styrene/p-(.alpha.-bromoethyl)-styrene copolymers. By copolymerization of such polymers with styrene, soluble graft copolymers or cross-linked products can be obtained. Braun and Keppler further disclose that styrene/p-(.alpha.-hydroxy-isopropyl)styrene copolymers can be dehydrated to obtain pendant isopropenyl groups.
The present invention discloses a means for synthesizing a polymer which contains a pendant unsaturated functionality by reacting an appropriately modified polymer with a small reactive molecule under phase transfer conditions in the presence of a base. The small molecule becomes attached to the polymeric substrate via a stable, nonhydrolyzable carbon-carbon double bond. The prior art does not suggest or disclose a process for the production of a polymer that contains pendant unsaturated functionality via a Wittig reaction.
It should be noted that the process of this invention allows the Wittig reaction to proceed in the presence of water. Heretofore, all Wittig reactions required strictly anhydrous solvents and reactants which would be a serious drawback when dealing with polymers. Another major point of interest in the process of the invention is that the Wittig reaction yields carbon-carbon double bond linkages. These linkages are very stable when compared to other chemical linkages often used in the binding of catalytic moieties to polymers.